1. Field
The present disclosure generally relates to magnetic recording and, in particular, to magnetic recording heads adapted for writing shingled tracks.
2. Description of the Related Art
One of the devices used to store data for long-term retention in a computer is referred to as a magnetic hard disk drive. A disk drive includes a magnetic rotating disk and read and/or write heads that move across the surface of the disk as it rotates. The read/write heads are biased toward the surface of the disk and when the disk rotates, the head floats on a cushion of the air that is moving with the disk. As this layer of air separates the moving disk surface from the relatively stationary read/write head in the same way that an oil bearing separates the moving parts in an engine, the layer of air and the surface of the read/write head are referred to as an “air bearing.” As the disk rotates under the read/write head, the write head generates a varying magnetic field to create transitions in the magnetic material of the disk according to signals from the processing circuitry of the computer.
Magnetic materials are characterized by a property called “coercivity” which is related to how easily the material is magnetized. A material having a low value of coercivity is considered magnetically “soft.” Conversely, a material having a high value of coercivity is considered magnetically “hard” and, once magnetized in a particular orientation, requires a strong field to re-orient the magnetization of the material. Magnetically hard materials are suitable for non-volatile data storage as a pattern of magnetization can be created in the material by a strong magnetic field, such as the field created by a magnetic recording head, and the pattern of magnetization will not change until rewritten by the strong magnetic field of the magnetic recording head.
A perpendicular recording system records data as magnetizations that are oriented perpendicular to the plane of the magnetic disk. A magnetic disk configured for use in this type of system has a magnetically soft underlayer and a thin magnetically hard surface layer. A perpendicular magnetic recording head has a write pole having a very small cross-section and a return pole that has a much larger cross-section. A strong magnetic field emerges from the write pole tip in a direction perpendicular to the magnetic disk surface and passes through the top layer of the disk, magnetizing the magnetically hard material of the top layer. The magnetic field then spreads out in the soft underlayer and returns to the return pole through a larger area of the top layer such that the strength of the field as it passes through the top layer is sufficiently low that it does not affect the magnetization of the top layer.
To increase the data density of magnetic hard disk drives, some drives utilize a “shingled” configuration of tracks, wherein adjacent tracks are partially overlapped in much the same way that rows of roof shingles are laid down. Writing a shingled track overwrites a portion of the previously written track that is immediately adjacent to it, requiring the tracks to be written in a specific order. The effective width of a track, which is the portion of the written track that retains the magnetization of the original signal after the following adjacent track is written, may be 10% or less of the width of a recording head. As a result, the magnetic field that writes to the final track is the part of the field around the trailing “final” corner. The quality of the magnetic field in a shingled-writing magnetic recording head is characterized by the radius of the magnetic field at the trailing corner.